Known sensor elements are configured, for example, as so-called planar sensors. These sensor elements include a solid electrolyte configured as a support, a measured gas electrode exposed to a measured gas, and, on the other side of the support, a reference gas electrode exposed to a reference gas. In a variety of applications, the sensor element must be heated to a specific temperature. It is known, for this purpose, to associate with the sensor element a heating device which usually has heating conductors extending in insulation layers beneath the electrode exposed to the reference gas.
To protect the electrode supply lead and the heater, it is known to equip the sensor element on both sides with a thick surface layer. The sensor elements are usually manufactured in batches by applying the individual functional layers of the sensor element in successive laminating processes (such as, for example, successive laminating silk screen printing processes) as areas and fine lines, and dicing into the individual sensor elements is then performed. The assemblage of films and layers yielding the sensor element is then sintered to produce a sensor element.
A disadvantage with the sensor elements discussed above is the fact that although it is possible, when the sensor elements are diced from the large-area assemblage of layers applied in film fashion, to cover the outermost layer by means of the surface layer, the end surfaces and edges of the functional layers that become exposed along the cut edges do not have the surface layer. When the sensor elements are used as intended, these end surfaces are thus exposed directly to the measured gas, which may, for example, correspond to the exhaust gas of an internal combustion engine. As a result, these uncovered end surfaces and edges offer an ideal surface for attack by the measured gas and by constituents contained in the measured gas. These can lead to decomposition of the exposed functional layers, and thus to an impairment of the characteristic curve of the sensor element.